An implant means a substitute for recovering lost human tissue. In dentistry, an implant generally means a substitute for recovering an original function of a lost tooth by planting and integrating a fixture into the alveolar bone, from which a natural dental root is missing, so as to replace a dental root of the lost tooth, and fixing an artificial tooth to the fixture.
Such dental implants may be classified according to a method of coupling an artificial tooth to a dental root. A screw-type implant, which is one of the dental implants, is manufactured by using a binding force of a screw. Conventionally, a screw-type implant or implant assembly consists of a fixture, an abutment and a prosthesis.
As shown in FIG. 1, a structure of a conventional dental implant prosthesis 100 includes an outer crown 110 that is formed of porcelain, and an inner crown 120 that is employed as a lower structure of the outer crown 110 and supports the outer crown 110. The inner crown 120 may be formed of various materials such as a gold (Au) alloy, a nickel (Ni)-chrome (Cr) alloy, zirconium (Zr), alumina, or titanium (Ti). The inner crown 120 may be manufactured by using a casting or cutting method, according to characteristics of each material. The inner crown 120 is deposited, and thus coupled to the outer crown 110 by using a mechanical and chemical mechanism.
An abutment 130 is conventionally formed of Ti or Zr, and is coupled to the inner crown 120 by using a dental adhesive. The abutment 130 is connected to an implant 140 that is installed in a mouth of a patient. The abutment 130 functions to support a prosthesis that is formed of the inner crown 120 and the outer crown 110.
If the outer crown 110 is formed of porcelain, instead of gold or another metal material, an artificial tooth may have a shape and color that are similar to a natural tooth. However, when used as the outer crown 110, the porcelain needs to have an overall even thickness of 0.3 to 3 mm due to its material characteristics, as shown in FIG. 2. An uneven thickness of porcelain may easily cause a fracture in porcelain. Particularly, if porcelain has a heavy thickness, a fracture may be easily caused in porcelain. Thus, an inner crown, which forms an internal structure of porcelain, needs to be precisely designed so that the porcelain may have an even thickness.
However, if an inner crown is manufactured by using a conventional casting method, it is not easy to precisely manufacture the inner crown. This is because since the casting method includes manufacturing a cast and melting metal into the cast, it is difficult to precisely manufacture an inner crown by using the casting method. Additionally, shrinkage may be caused in a hardening process that is performed after casting. Particularly, the casting may be affected by a lot of factors, such that the casting method greatly depends on the skill of a worker. Furthermore, there is a possibility that the casting may fail, or an environmental pollution may be caused.
Additionally, it takes about 8 hours for each cycle to manufacture an inner crown. Accordingly, it takes a long time to manufacture an inner crown, and thus, a manufacturing cost is increased.